Check out used tiny/mini/micro desktops on eBay. Loads of info here: https://www.servethehome.com/introducing-project-tinyminimicro-home-lab-revolution/
Only downside is going to be no GPU for the AI workload. Maybe some of the later AMD APUs could cut it. If not, all three major manufacturers have SFF variants that are pretty much the same hardware in a little bigger case. Those will accept smaller off the shelf GPUs.
2nd this. Cheap, upgrade-able, more powerful than the pi, and not limited to ARM. Only thing the Pi has on this is power consumption and GPIO.
Consider a used HP Elite desk SFF (small form factor) with a 6th Gen or later Intel CPU (or the equivalent from Dell or Lenovo). Space for 2x 3.5 HDD for data, an nvme m.2 slot for your OS drive, and a couple of pcie expansion slots.
1.) it's cheap and replacement parts are plentiful 2.) 6th+ gen Intel CPUs have Quick Sync for hardware accelerated transcoding 3.) fast interface for the OS drive, and room for a pair of multi TB HDDs in raid. 4.) some expandability 5.) power draw isn't horrible, but nor is it great.
OS wise, lots of options. Ubuntu server LTS is my general go to because it's easy to Google stuff for and is stable. And I don't need a desktop environment. I then run the services in docker.
Note about Intel Quick Sync when running headless: you may need a display emulator to get the system to enable it. The HP bios (and maybe some others) don't have the option to permanently enable quick sync. The display emulator tricks it into thinking a display is plugged in. You can get them on Amazon for under $10.
Vaultwarden is pretty game changing. No more reusing passwords and they aren't in the cloud.
Pretty much this. Combined with how easy it is to install VaultWarden (docker ftw), it was a no brainer for me.
Also, my little home server is a WAY less juicy target for someone looking to steal and sell a bunch of passwords.
Been running it for probably about 2 years now. No ISP outages but a couple self-inflicted ones. Didn't even notice the outages in the BitWarden app/extension.